Thermal loading of pistons within cylinders of an engine has increased in response to demands for higher power output and lower emissions. However, increased thermal loading of pistons can cause issues such as, engine seizures and engine degradation. Furthermore, designing pistons to avoid such degradation may involve higher-cost materials and manufacturing methods, or compromises in other desired attributes.
Lubrication systems may be used to cool various engine components during a dynamic range of engine operating conditions. For example, pistons may be cooled via piston cooling jets wherein oil is sprayed at an underside of the piston. An example piston cooling assembly is described by Chimonides et al. in U.S. Pat. No. 6,298,810 wherein an oil nozzle is located on an engine block to supply oil to the underside of the piston. The inventors herein have recognized potential issues with piston cooling via piston cooling jets. For example, piston cooling jets may be operated in a continuous manner, such that cooling oil is constantly sprayed from the oil nozzle. As such, a larger proportion of the oil may be sprayed without cooling the piston due to the reciprocating motion of the piston. For example, much of the cooling oil may not reach the piston when the piston is at top dead center position in the cylinder. Thus, larger amounts of oil may be sprayed towards the piston in order to effectively cool it. The pump pressurizing the oil may perform extra work, leading to a reduction in engine efficiency.
The inventors herein have recognized the above issues and identified approaches to at least partly address the issues. In one example, the issues described above may be at least partially addressed by a method for an engine, comprising repeatedly activating an oil supply only during a part of a cylinder cycle synchronous with a frequency of piston reciprocating motion. In this way, oil supply may be provided during a portion of the engine cycle and not in a continuous manner.
In another example, a system may be provided comprising an engine including a cylinder, a piston capable of reciprocating motion arranged within the cylinder, the piston including a skirt, and a lubrication system comprising an oil gallery, a pump, a piston cooling assembly fluidically coupled to the oil gallery, the piston cooling assembly positioned beneath the piston, and a poppet valve substantially blocking an opening of a nozzle of the piston cooling assembly, wherein the opening of the nozzle is unblocked by displacing the poppet valve via the skirt of the piston to initiate an oil supply through the piston cooling assembly. In this way, the piston actuates oil supply via displacing the poppet valve.
In another example, a method for an engine may be provided, comprising delivering oil to a piston during a first portion of a cylinder cycle, the piston arranged within a cylinder of the engine, and not delivering the oil to the piston during a second portion of the cylinder cycle.
For example, an engine may comprise at least one cylinder with a reciprocating piston arranged within the at least one cylinder. A piston cooling assembly including a valve body, poppet valve, and a nozzle may be positioned near the piston. The piston cooling assembly may be positioned such that during a first portion of an engine cycle, a skirt of the piston displaces the poppet valve of the piston cooling assembly allowing a flow of oil from the nozzle. The first portion of the cylinder cycle may include a duration when the piston is substantially at bottom dead center position such as during each of an intake stroke and an expansion stroke of the cylinder cycle. Further, oil flow may not be initiated during a second portion of the cylinder cycle. The second portion of the cylinder cycle may include a duration when the piston is substantially away from bottom dead center position.
In this way, a piston in an engine may be cooled to reduce degradation. By using piston motion to actuate a cooling oil supply, additional control mechanisms may not be desired. As such, the oil supply is actuated only during a portion of a cylinder cycle when the piston is near the piston cooling assembly. Thus, oil flow may be directed to and may cool the piston in a more reliable manner, with less waste of pressurized oil. Overall, the piston may be cooled more efficiently with less oil pump work, enabling improved efficiency of the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.